Monday, October 01, 2007

How does light pollution affect the world's skies?

Stargazers around the world are being asked to help scientists map light pollution. The project, dubbed the Great World Wide Star Count, takes place from 1 to 15 October and is designed to raise awareness about the impact of artificial lighting on the night sky.

The two-week-long event encourages everybody to look skyward between the hours of 7 and 9 pm local time. Participants in the Northern Hemisphere will seek out the constellation Cygnus the swan (pictured), while those in the Southern Hemisphere will observe Sagittarius the archer.

After waiting at least 15 minutes for their eyes to adjust to the darkness, stargazers will match their observations with magnitude charts downloaded from the Great World Wide Star Count Web site. The site also offers interactive star maps for finding the constellations as well as information on how to determine your longitude and latitude. A downloadable activity guide that includes step-by-step instructions, star maps and a reporting form is also available.

With observational data in hand, participants will add their findings to an online database. Stargazers plagued with overcast skies are encouraged to input data about cloud conditions instead.

You can learn more about light pollution and its effects on the night sky, as well as its biological effects on the environment and potentially human health, from the International Dark-Sky Association.

Do you plan to participate? What are your thoughts on light pollution? Have you ever seen the night sky from a true dark sky site?

Wednesday, May 30, 2007

How dark are your skies?

How dark is the night sky where you live? "Not very" would be my hand-wavey answer for Boston, but I'd be hard pressed to tell you anything more precise. Soon, though, there may be maps of the sky's brightness in cities and towns and rural areas all over the world, thanks to the efforts of citizen-scientists armed with handheld light meters.

So far, 135 of the digital sky meters have been distributed to teachers, students, museum personnel and amateur astronomers around the world in a programme called the Globe at Night. They have returned an estimated 1000 measurements since March, and the results are not surprising – the skies are brightest above the densest urban areas and get progressively darker as you travel farther away from cities (see the data from Washington, DC, at left – yellow and green areas have brighter night skies than blue ones).

The data is "the start of a baseline of measurements that can be used to track changes over time, to compare as 'ground truth' with satellite measurements of dark skies, and to search for safe urban 'dark sky oases' that can be preserved", says Stephen Pompea of the National Optical Astronomy Observatory (NOAO) in Tucson, Arizona, US.

The Globe at Night originally started in 2006 as a naked-eye observational programme to measure the brightness of the night sky. In the 'classic' version of the project, volunteers would match the appearance of the constellation Orion with illustrations during a week when the Moon did not appear bright.

Nearly 4600 measurements were reported in 2006, and about 8500 were submitted this year. Organisers were delighted with the results, but Pompea said the project came with inherent uncertainties. "Older people's eyes are not quite the same as younger people's eyes," he told reporters at a meeting of the American Astronomical Society this week in Honolulu, Hawaii, US.

NOAO colleague Connie Walker says the new light meters are much more precise. "You can get to two decimal places with meters as opposed to what you can do with your eye –there's no ageing eye influence."

The meter project was funded with half of a $32,000 grant from the National Science Foundation, and project organisers are planning to buy more meters with the remaining funds.

If it takes off, I think it will do more than raise awareness about the growing problem of light pollution and track just how bad the problem is. It will get people outside, looking up and marvelling at what they see (even if it's just the Moon).